The above output shows that there are seven USB root hubs available on my system, but only two of these support the high-speed USB 2.0 protocol. In order to benefit from high-speed data throughput the external USB disk needs to be connected to a bus with a 2.0 root hub. It also helps if you attach one device per bus so they do not share bus bandwidth.

The Shuttle SA76G2 specs claim that all the USB ports are 2.0 compliant, but ‘lsusb’ reveals that Fedora 10 detects only two 2.0 root hubs. After moving the external drive between the physical USB ports I identified a port which was attached to a 2.0 root hub and since then data throughput has been excellent.